The present invention relates to an optical recording and/or reproducing apparatus such as optical disc apparatus, and in particular, relates to an optical system for such optical recording and reproducing apparatus.
Optical disc apparatus such as opto-magnetic disc apparatus has come to be widely used for text data file for the recording of computer data.
Generally, since the optical system for the opto-magnetical disc apparatus is complicated, the weight of the system increases. This fact results in a major problem in realizing a high speed access. As the means for solving this drawback, there is known a separation-type system such that only an objective lens of the optical system, an actuator unit for driving the lens and relay prism for directing a laser beam to the lens are mounted on a feed/or tracking mechanism, to thus construct a movable unit transferred in a radial direction of the disc, and that other portion of the optical system are fixed to the base of the recording and reproducing apparatus to thereby reduce the weight of the movable unit to much degree, thus performing a high-speed access.
In case of recording or reproducing, the disc is driven to rotate at a high speed (such as 3,600 rpm) and irradiating the light spot of the laser beam to the disc and performing the optical recording and reproducing requires that the light spot be moved in the direction of the diameter of the disc and with the range from the outer diameter to the inner diameter of the disc. In addition, when there is the vibration of the surface of the disc, the point of focus of the light spot must automatically track on the disc.
the movement of the light spot in the direction of the radius (feed operation) uses a tracking servo actuator and is performed by moving the relay prism and the objective lens. In addition, the operation so that the point of focus tracks the disc uses a focus servo actuator and is performed by moving the objective lens up and down.
These tracking servo and focus servo actions should desirably be performed at a high access speed with respect to the disc, and have improved controllability of the objective lens without causing vibration and the like. In addition, it is also desirable that the servo actuator be small and lightweight.